This work attempts to determine the nature of sustained attention and to deter-mine the parameters of task-unrelated images and thoughts (TUITS) as well as related mental activity such as insight, attention and sustained attention as phenomena, their relationships amongst one another, and their susceptibility to the influence of aging in adulthood. These goals are accomplished through the use of controlled laboratory studies and retrospective questionnaires. This year's findings were that (a) extended practice on a vigilance task, with typical exposure times, is best fit by a hyperbolic functional relationship derived from an accumulation model of learning in which age significantly affects final asymptotic performance but which does not affect learning rate; (b) TUIT likelihood is inversely related to performance on a vigilance task an reflects the capacity demands of the vigilance task. The study of task-unrelated images and thoughts in adults, along with variable which may moderate their occurrence, e.g., age, intelligence, task structure, etc., may aid us in understanding the fundamental processes which underlie all thinking. Sustained attention as a skill involves both alertness and concentration over long periods of time. This skill plays an important role in both daily living and in the job market place, e.g., jobs requiring inspection. his research provides us with information on how age influences the use and acquisition of that skill as well as how alertness and concentration are susceptible to aging influences.